"Vietnam must stop all action that violates the Chinese sovereignty," Chinese Foreign Ministry spokesman Hong Lei said in a statement here reacting to allegations by Vietnam that Chinese fishing boat "intentionally" ramming into its exploration ship.

China has indisputable sovereignty over the Nansha Islands and the surrounding waters, which belong to the South China Sea, Hong said asserting that Chinese fishermen have been fishing on the Vanguard Bank of the Nansha Islands from generation to generation.

However, Chinese fishing boats, while operating in the above waters, were chased away by armed Vietnamese ships on Thursday morning.

Amid the chasing turmoil, the fishing net of one of the Chinese fishing boats got tangled with the cables of a Vietnamese oil exploring vessel, which was operating illegally in the same water area, he said.

Regardless of the safety of the Chinese fishermen, the oil exploration boat continued dragging the Chinese fishing boat for more than one hour, with the latter's tail facing the front.

The Chinese fishermen, therefore, had to cut off the fishing net before the two vessels lost contact.

This has seriously endangered the safety of the Chinese fishermen, Hong said.

The oil explorations on the Vanguard Bank and chasing away of the Chinese boats by the Vietnamese side have grossly infringed the Chinese sovereignty and maritime rights, he said.

"Vietnam must stop all action that violates the Chinese sovereignty. No more action is allowed to endanger the safety of the Chinese fishermen and their properties.

"And no action should be taken to amplify the dispute and make it more complicated," he said.